It is known to cool the reciprocating piston of an engine by directing a stream of oil onto its underside. The nozzle used to direct the oil stream may be a so-called dowel nozzle, which is a carefully shaped and positioned tube fed from a dedicated oil gallery and aiming a jet of oil onto a target point on the piston. Alternatively, the nozzle may be in the form of a plastic nozzle inserted into a bore in the saddle of a main bearing and fed from an annular oil groove in the upper main bearing shell. These two types of nozzle are designed to operate with different oil flow rates and the nozzle fed from a dedicated oil gallery requires an oil pump of higher output.
If different variants of the same engine produced by a manufacturer are designed to operate with different types of oil nozzle, the spray pattern achieved by supplying oil to a plastic nozzle using a higher output pump intended for a dowel nozzle results in an oil plume angle that is so large that the oil achieves a negligible cooling effect.
Simply reducing the bore of the nozzle itself does not correct this problem but will probably increase the plume angle still further due to the higher dynamic pressure across the plastic nozzle.